1. Field of the Invention
The present invention relates generally to the field of electromagnetic shielding, and in particular, to a surface mount spring gasket to assist electrical connectivity between components that must be joined to provide electromagnetic shielding.
2. Description of the Background Art
Electromagnetic interference (EMI) is a common problem faced during the operation of electronic equipment. EMI is unwanted electromagnetic energy entering or emitting from a specific piece of electronic equipment, thereby causing interference. EMI can cause that piece of electronic equipment or electronic equipment nearby to function improperly or to not function at all.
Typically, electronic equipment is housed within metallic cabinets to help reduce EMI problems. In order to reduce cost and weight, for example, some cabinets are made out of non-conductive plastic, thereby establishing the need for smaller EMI housings. Additionally, it is know that small EMI housings are sometimes required to shield electrical components mounted on a printed circuit board (PCB) from EMI caused by other electrical components also mounted on the PCB. EMI housings for PCBs generally comprise a planar sheet metal structure having a top and at least four downward facing walls which are mounted on a PCB so as to enclose therein the electronic components for which EMI shielding is required. Unfortunately, the labor involved in the fabrication, assembly and connection of such planar sheet metal parts to form the EMI housing and its connection with the PCB is significant, thereby causing a relatively high cost for the EMI shielding portion of the electronic equipment. It is known, for example from U.S. Pat. No. 5,418,685 issued May 23, 1995, to provide a housing that is comprised of two halves, an upper and lower half, each designed to be positioned on opposing sides of a PCB and for being joined together so as to form an EMI housing including internal walls for various portions of the PCB. Unfortunately, unless the housing halves are manufactured with extreme precision, their flatness tolerance at the wall portions where they join with the PCB are generally insufficient to make an electrical contact which is sufficient for providing acceptable EMI shielding. Although it is well known to provide various types of gaskets as "fillers" between the PCB contact areas (such as ground plane conductor paths) and the downward facing walls of the EMI housing halves, current gaskets are somewhat unacceptable. The reasons for their unacceptability generally flow from the fact that the housing halves include several internal walls that need to make good contact with the PCB. The walls includes gaps in it where conductors and conductor paths enter and exit from the PCB. These gaps and internal walls add substantial difficulty to finding an acceptable gasket since some wall segments are as small as 0.3 inches long and the ground plane conductor on the PCB are typically only 0.1 inches wide. The use of commercially available gaskets, such as the widely used metal strip commonly referred to as "finger stock", is inappropriate due to its relatively large size compared with the small sized conductors and housing walls of such small size. Intensive labor actions are involved for cutting, fitting and installing such gaskets on conductors and housing walls of such small size. Alternatively, various conductive elastomer compounds can be used, but again the addition of conductive elastomers adds significant expense to the assembly of the product. An added requirement is that it is often required that the PCB be repaired or serviced and therefore the gasket must be reusable.
In view of the foregoing, it is seen that it would be desirable to provide a spring gasket for use in joining a PCB with an EMI enclosure that is particularly well suited for EMI housings having small walls and/or walls with small openings. Furthermore, the new spring gasket should be reusable and more economical.